Have a series of rotating blades in the toilet bowl to finely chop the waste product before it's flushed. As a positive side effect it'll stop people spending too much time in the lav. and will stop pets drinking from the toilet (at least they'll only do it the once!)

In Bruges five years ago we stayed at a B&B which had something like this. We were asked not to flush the toilet during the hours when people would be sleeping. Evidently the walls were too narrow for regular size pipes, and the "material" had to be chopped up to fit down the drain. Flushing was really noisy.

In some medieval castles they have a version of this. A toilet seat-type aperture set into the stone wall. Simply crap in the hole, and your shit plummets 20 feet to the ground outside, where it will be thoroughly pulverised by the impact or passing cart wheels.